When Lawrence Klein, an accomplished young economist at the University of Michigan, applied for tenure in 1954 after serving on the faculty for five years, he found his way blocked. He was quizzed about his brief membership of the Communist Party ten years before, when the Soviet ­Union was fighting alongside the United States and Britain against Nazism.

Klein’s accusers, bolstered by the congressional hearings led by Senator Joseph McCarthy over the suspected communist infiltration of American institutions, held up the appointment. Angry and irritated to be ­hounded for his ­beliefs, Klein abandoned the US and headed for Oxford University’s